Heavy metals are known as a hazardous group of pollutants. The contamination by heavy metals causes a serious problem because they cannot be naturally degraded like organic pollutants and they are accumulated in different parts of the food chain. Physical and chemical methods have been proposed for the removal of these pollutants. Nevertheless, they have some disadvantages, among them cost-effectiveness limitations, generation of hazardous by-products or inefficiency when concentration of polluted materials is below 100 mg/l. Biological methods help to avoid these drawbacks since they are easy to operate, do not produce secondary pollution and show higher efficiency at low metalconcentrations. Microorganisms and plants are usually used for the removal of heavy metals [1,5,7]. Mechanisms by which microorganisms act on heavy metals include biosorption, bioleaching, biomineralization, intracellular accumulation andenzyme-catalyzed transformations. Microalgae have been found to be efficient biosorbents of metal ions from wastewater, owing to their low cost, prompt availability, relatively high specific surface area and good binding affinity [3,4]. Being used in electroplating (anti-corrosion agent), alloys, pigments in paints, organic synthesis, agriculture, zinc falls within the aquatic environment, creating and advanced level of pollution [2, 6]. To determine the biosorption of Zn cations by Spirulina platensis 0.75 g of biomass were suspended in 100 mL of ZnSO4·7H2O solution (concentration 0.34 mM and 3.4 mM) in 250-mL glass flasks on a rotary shaker set at 100 rpm. The process of zinc adsorption was studied during 1 hour. Samples were collected in 5, 15, 30 and 60 minutes. For samples elemental content determination neutron activation analysis (NAA) at the pulsed fast reactor IBR-2 (FLNP JINR, Dubna) was used. Samples with concentration of ZnSO4·7H2O 0.34 mM were irradiated for 2 days and their activity measured in 4 days. The zinc content was determined by γ-line with the energy 1115.5 keV of isotope 65Zn. For samples with concentration of ZnSO4·7H2O 3.4 mM the irradiation time was 30 min and Zn concentration was determined by γ-line with the energy 438.6 keV of isotope 69mZn. The NAA data processing and determination of element concentrations were performed using software developed in FLNP JINR. The conventional techniques to remove toxic metals such as ion exchange and precipitation are considered to be inefficient and too expensive when the zinc ion concentration in the aquatic environment is lower than 100 mg/l. In our case in the first experiment the concentration of zinc was 22.6 mg/l. In the second experiment the concentration of zinc in solution was higher. In this case the microbial metal removal and traditional technologies of water purification can be efficiently applied. In the case of zinc sulfate with a concentration of 0.34 mM the zinc content in biomass during the first 5 min of interaction grows up from 50 to 900 μg/g and further accumulation is observed, no saturation occurs. The rate of biosorption of zinc from solutions after the first five minutes of contact decreases gradually, but stable growth is recorded within 60 minutes of contact. From the solution of zinc sulfate (0.34 mM) the spirulina biomass accumulated about 56% of zinc ions (1700 μg/g). At the ZnSO4 concentration of 3.4 mM (Fig.1b) the rate of metal removal from solution was very rapid in the first 5 min (from 50 to 9000 μg/g) then it did not change significantly. In this case the spirulina biomass accumulated 6.75mg of zinc ions from 22.6mg present in 100 ml of solution. The extension of the contact time of interaction of 3.4mM zinc sulfate solution with the spirulina biomass does not lead to the additional accumulation of the metal ions. Thus, in the case of a high concentration of zinc ions in the solution the efficiency of the spirulina biomass as a sorbent is lower. The potential application of microorganisms for water treatment is an efficient method. Spirulina biomass can be successfully used for zinc removal from wastewater at low zinc concentration, when conventional techniques are unprofitable. Spirulina cyanobacteria can be efficiently used for the processes of water post-treatment and as a matrix for zinc-containing drugs The work was funancially supported by JINR GRANT № 13-402-03 and institutional project 11.817.08.18F References: [1] Farooq, U.; Kozinski, J. A.; Ain Khan, M.; Athar, M. Biosorption of heavy metal ions using wheat based biosorbents – A review of the recent literature. In: Bioresour. Technol. 2010, 101, 5043–5053. [2] King, P.; Anuradha, K.; Beena Lahari, S.; Prasanna Kumar, Y.; Prasad, V. S. R. K. Biosorption of zinc from aqueous solution using Azadirachta indica bark: Equilibrium and kinetic studies. In: J. Hazard. Mater. 2008, 152, 324–329. [3] Monteiro, C. M.; Castro, P. M. L.; Malcata, F. X. Biosorption of zinc ions from aqueous solution by the microalga Scenedesmus obliquus. In: Environ. Chem. Lett. 2011, 9(2), 169- 176. [4] Morsy, F. M.; Hassan, S. H. A.; Koutb, M. Biosorption of Cd(II) and Zn(II) by Nostoc commune: Isotherm and Kinetics Studies. In: CLEAN – Soil, Air, Water. 2011, 39 (7), 680- 687. [5] Vecchi,o A.; Finoli, C.; Di Simine, D.; Andreoni, V. Heavy metal biosorption by bacterial cells. In: Fresenius J. Anal. Chem. 1998, 361, 338–342. [6] Venkateswarlu, P.; Vijaya Durga, G.; Chitti Babu, N.; Venkateswara Rao, M. Biosorption of Zn(II) from an aqueous solution by Erythrina variegata orientalis leaf powder. In: Int. J. Phys. Sci. 2008, 3 (9), 197-204. [7] Vijayaraghavan, K.; Yun, Y. S. Bacterial biosorbents and biosorption. In: Biotechnol. Adv. 2008, 26, 266–291.
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